Rinse pork and pat dry; season with salt and pepper. Heat 2 tablespoons oil in a heavy 5-quart pot over moderately high heat until hot but not smoking. Add pork, in 3 batches, and cook, turning, until golden brown, about 6 minutes per batch (adding oil, 1 tablespoon at a time, as needed). Transfer, as cooked, with a slotted spoon to a bowl, leaving fat in pot. Rinse chicken and pat dry; season with salt and pepper. Add 1-1/2 tablespoons oil to fat in pot and heat over moderately high heat. Add chicken and cook, turning, until golden brown, about 3 minutes. Transfer with a slotted spoon to bowl with pork. Add potatoes, onion and garlic to pot; cook over moderately high heat until onion is softened, about 3 minutes. Stir in broth, corn, adobo sauce and peanut butter. Return pork and chicken to pot with any drippings and push into liquid. Simmer, uncovered, stirring occasionally, until slightly thickened, meat is cooked through and potatoes are fork-tender, 35 minutes; salt and pepper to taste. To serve, ladle stew into bowls and garnish with cilantro, if desired.